                      (into (pop q)
                            (for [d (keys nv)
                                  :let [e1 (.get nv d)
-                                       e2 (.get nw (.times d op))]
-                                 :when e2]
+                                       e2 (.get nw (.times d op))]]
                              [e1 e2]))))))))))
 
 (defn symmetries [net]

            (empty? q)
            src2img

            (= b (src2img a))
            (recur src2img (pop q))
            

  (when (.isUnimodularIntegerMatrix M)
    (let [sigs (node-signatures net)
          d (.minus (first (first (sigs w))) (first (first (sigs v))))
          op (.times (Operator. (extend-matrix M)) (Operator. d))]
      (loop [src2img {}
             q (conj empty-queue [v w])]
        (let [[a b] (first q)]
